In our European patent specification No 0 289 240 there is disclosed apparatus for forming flakes of material from a heated stream of molten material. The apparatus comprises means for feeding the stream in a downwards direction into a rotating cup, the cup being arranged with its open mouth facing upwardly such that molten material within the cup is caused to flow over the upper edges of the cup and flow outwards in a radial direction due to centrifugal force. The apparatus also includes a pair of spaced apart substantially parallel plates arranged about the cup such that the material leaving the cup by centrifugal force passes through a gap defined between the plates. The plates are mounted within a vacuum chamber arranged such that a vacuum is applied to the space between the plates to draw air from outside the chamber between the plates in a radial direction to prevent the molten material from touching the sides of the plates and to cool material until it reaches a solid state pulling the material in a radial direction thereby keeping the material in the form of a flat film and breaking it into small platelets.
In the production of glass or ceramic fibre or flake the thickness is determined in part by the temperature and volume of the flow stream entering the spinning device producing the product. As the flow stream is necessarily open to atmosphere between an outlet from which the stream emerges and the spinning device, it is subject to heat loss and variation in temperature. The loss of heat is detrimental to the production of thin fibres or flake, particularly in the sub-micron range and changes in temperature as small as one degree cause variation in thickness. The viscosity of the glass mass within a source tank or reservoir is determined by temperature variations which in turn cause changes in mass flow through the outlet from which the stream emerges. Additional mass flow changes are caused by head variations within the tank.
Furthermore, in order to compensate for the heat loss outside the source tank, the temperature within the tank may need to be higher than the stream temperature by some hundreds of degrees. This is not only energy wasteful but may cause severe erosion and corrosion of the refractory lining within the tank.